1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for depositing thin films on semiconductor substrates using chemical vapor deposition (CVD). More particularly, embodiments of the present invention relate to an apparatus and method for eliminating the “first wafer effect” for plasma enhanced chemical vapor deposition (PECVD).
2. Description of the Related Art
Semiconductor fabrication includes a series of processes used to fabricate multilayered features on semiconductor substrates. The process chambers may include, for example, substrate preconditioning chambers, cleaning chambers, bake chambers, chill chambers, chemical vapor deposition chambers, physical vapor deposition chambers, etch chambers, electrochemical plating chambers, and the like. Successful operation requires a stream of substrates to be processed among the chambers, which conducts steady state performance on each one of the stream of substrates.
During semiconductor fabrication, materials, such as oxides, e.g., carbon doped oxides, are typically deposited on a substrate in a processing chamber, such as a deposition chamber, e.g., a chemical vapor deposition (CVD) chamber. In a typical CVD process, a substrate is exposed to one or more volatile precursors flown into the CVD chamber, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, and are removed by gas flow through the CVD chamber. In a plasma enhanced chemical vapor deposition (PEVCD), a plasma is generated in the CVD chamber to enhance chemical reaction rates of the precursors. PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors. A steady state performance of a CVD or PECVD chamber generally requires all the hardware components, such as, for example, the liquid flow meter for controlling the flow rate, the faceplate for generating the plasma within the chamber, and the pedestal for supporting and heating the substrate, to render ideal performance. However, after an extended idle time, a CVD chamber may need to successively perform deposition and cleaning processes on several substrates before it reaches the steady state performance. As a result, the deposited film properties on the first several substrates are significantly different from ideal, which is often referred as the “first wafer effect”. Sometimes, it needs to process up to 12 substrates before reaching the steady state.
The “first wafer effect” may be attributed to several reasons. The faceplate, which generally has a radio frequency (RF) feedthrough providing a bias potential to generate a plasma, has a temperature much lower for the first substrates that leads to a lower deposition rate. Additionally, after a long idle time, the liquid flow meter (LFM) calibration factor can vary up to 5%, which leads to unsteady precursor supply rate during the first substrates. Further, the faceplate may also be non-uniformly heated which causes non-uniform deposition across the substrate surface.
In the state of the art system, the “first wafer effect” is reduced by implementation of a “Go-Clean” process prior to processing the first substrate after a period of idle time. The state of the art “Go-Clean” process generally includes a plasma heating step, a deposition step, a clean step and a season step. The state of the art “Go-Clean” process reduces the “first wafer effect”, but typically process 4 to 6 substrates after the “Go-Clean” before reaching the steady state.
Therefore, there is a need to develop an apparatus and method that minimize or eliminate the “first wafer effect” in CVD process.